fix: log /register listener failures instead of discarding them

A failing user.Register or user.Created listener is logged at Error level
with the user ID; the committed registration still succeeds.

register_test.go

@@ -2,6 +2,7 @@ package user
 
 import (
 	"encoding/json"
+	"errors"
 	"net/http"
 	"net/http/httptest"
 	"os"
@@ -248,6 +249,27 @@ func TestRegisterEventPayload(t *testing.T) {
 	}
 }
 
+// TestRegisterListenerErrors: failing register and created listeners are
+// logged and neither fail nor undo the registration.
+func TestRegisterListenerErrors(t *testing.T) {
+	app, gdb := sessionApp(t, "0s")
+	disableRegisterThrottle(t, app)
+	app.Events.Listen[*classes.RegisterEvent]("failing-register", func(context.Context, *classes.RegisterEvent) error {
+		return errors.New("register listener down")
+	})
+	app.Events.Listen[*classes.CreatedEvent]("failing-created", func(context.Context, *classes.CreatedEvent) error {
+		return errors.New("created listener down")
+	})
+	rec := postJSON(t, controllers.Register(app), "/_user/api/v1/register", `{"email":"listener-fail@example.test","password":"correct-horse"}`)
+	if rec.Code != http.StatusOK || !strings.Contains(rec.Body.String(), `"token"`) {
+		t.Fatalf("register %d %s", rec.Code, rec.Body.String())
+	}
+	var count int64
+	if err := gdb.Model(&models.User{}).Where("email = ?", "listener-fail@example.test").Count(&count).Error; err != nil || count != 1 {
+		t.Fatalf("stored users = %d, %v", count, err)
+	}
+}
+
 // TestRegisterIgnoresProtectedFields: a registration body sets only the
 // RegisterFillable columns. Organisation membership, the IP columns and the
 // account flags in the body are ignored, over HTTP and through RegisterUser,